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1. The authors investigated the role of thermoregulation mechanisms and thermal limits on thermal niche differentiation in two hierarchical similar Eucraniini dung beetle assemblages inhabiting arid environments in north-western Argentina. Both dung beetle assemblages showed temporal and thermal niche segregation between all sympatric species, minimising overlap during their daily activity and soil temperature preferences. 2. Thermal tolerance of Eucraniini species was partially modulated by behavioural adaptations and complementary thermoregulatory mechanisms related to eliminating the temperature excess, increasing the metabolic rate promoting an effective regulation of the excess heat that permitted a decrease in their body temperature by evaporative cooling. Based on the physiological syndromes obtained, the authors found a greatest interspecific differentiation that allows us to differentiate each species using ecophysiological traits. Interspecific body size differences in sympatric Eucraniini contributed greatly to the metabolic capacity of individuals to thermoregulate. 3. Eucranium species, the largest species showed the lowest capacity to respond to thermal stress decreasing heat excess temperature, presenting the lowest thermal limit values coinciding with a ‘minithermy’ strategy that explains the preferred lower soil temperatures around 30°C. On the contrary, Anomiopsoides species showed a clear adaptation to being active during periods of the day in which the soil temperature reached over 50°C, adopting a strategy of ‘maxithermy’ by foraging when temperatures are closer to their thermal limits. 4. In conclusion, it can be determined that ecophysiological syndromes related to thermal stress regulation and thermal limits allowed a displacement in thermal niche dimension, minimising interspecific competition and so allowing species coexistence in Eucraniini dung beetles.

In heterotherm insects, endothermy implies a high energy cost due to the generation and regulation of body temperature during different activities such as flight, food location, fighting and even walking. We studied the thermoregulation process and the cost of the thermoregulation strategies in two sympatric dung beetles, Sulcophanaeus batesi and S. imperator under heat and cold stress conditions. We used a set of physiological variables to exemplify the capacity of thermolimit respirometry combined with infrared thermography to derive relevant variables capable of describing different thermoregulation syndromes. Habitat use and thermal niche differed notably between S. batesi and S. imperator, reflecting their contrasted thermal requirements. In S. imperator, thermal specialization for high temperatures was observed, being active mainly during the warmer period of the day. On the other hand, thermal adaptation in S. batesi allows its preference for cold exhibiting a morning activity periods, avoiding higher temperatures. The thermophilic strategy used by Sulcophanaeus imperator minimized the energy expenditure produced during the cooling of the body by respiration without thereby endangering higher thermal limits. In this case, S. batesi, the species with a preference for the coldest environments, presented the lowest thermal limits, although the energy cost needed to stay active during cooling was significantly lower than that in S. imperator. Sulcophanaeus imperator and S. batesi showed evident ‘economizing’ strategies associated with hot and cold environmental conditions, respectively. In contrast, if both species experience a deviation from their thermal optimum, a decrement in their performance could be produced.